Quantitative ultra-low temperature autoradiography, ultra-low temperature microdissection and the fluorescence microscopy of fluorescein-conjugated macromolecules are being used in studies of intracellular transport. These include studies of the permeability of the nuclear envelope, the nucleocytoplasmic distribution of solutes, and sorption-desorption processes. The experiments are in minimally disturbed cells, with large nuclei; especially the amphibian oocyte and the dipteran salivary gland cell.